Jude uses a nautical theme here. Thus, "hidden reefs" (a variant translation supported by the Greek) is preferable to "spots." The apostle says that these false teachers are like hidden reefs at our socials; they are just under the surface, waiting for the unsuspecting Christian to come along and be shipwrecked upon them.
Paul dealt directly with a similar problem in Corinth (I Corinthians 11:17-22). They held "feasts without the fear of God." They do not fear the oversight and punishment of God, that what He says will happen as a result of their self-satisfying sins, which may take many forms. Gorging themselves is only one part of it. Worse is that they use these occasions to shipwreck people, to undermine their faith, to whisper in their ear to get them thinking along the wrong lines.
Jude says that they serve only themselves. Again, this phrase is poorly translated due to being interpreted rather than given literally. It should be "shepherding only themselves." Ezekiel 34:1-5, 10 alludes to the same problem Jude faced.
Verse 12 also says that these false shepherds outwardly show promise of producing fruit, of bringing rain, but they never do. Paul indeed calls some of Satan's ministers "angels of light" (II Corinthians 11:13-15), but their fruit shows they possess nothing of godly, spiritual substance (Matthew 7:15-20). They will never produce godly fruit. They look good on the outside, but on the inside they are corrupt and full of bones (Matthew 23:27). When Jude describes them as "twice dead," he may be refering to the second death (Revelation 20:14; 21:8)—that they will die physically once, and then they will die spiritually the second time. It is at least saying they are well on the road to the Lake of Fire.
Hebrews 10:26-31 says plainly that once we have been forgiven and redeemed by the blood of Christ, there is no going back. If we continue to sin as a way of life, there is no second redemption, and all we face is the vengeance of God, who is a consuming fire. This is what Jude is trying to get across in relation to these false ministers.
Richard T. Ritenbaugh
Other Forerunner Commentary entries containing Jude 1:12:
2 Kings 4:27-31